Process for the assembly of glass devices subjected to high temperatures, compositions therefor and novel polymers for rheological control of such compositions

ABSTRACT

Cationically curable adhesives and sealants with increased viscosities and improved rheological control and good storage stability are prepared using a cationically curable monomer and a thickening polymer which is the alkylation reaction product of poly(4-hydroxystyrene) or poly(2-hydroxystyrene) with a compound RX where R is allyl, methallyl, crotyl or prenyl and X is Cl, Br or I. The cationically curable monomer suitably includes at least one alkenyloxystyrene monomer. Such thickened adhesives are useful as edge sealants for flat panel display devices. A-stage curing of the adhesive with UV irradiation allows for near ambient temperature fixturing of the device assemblies and B-stage thermal curing of the adhesive can be conducted at much lower temperatures than are needed for glass frit sealants. The B-stage cured products have thermal resistance, outgassing and substrate adhesion properties adequate for flat panel display devices.

This application is a division of U.S. application 08/723,087, filedOct. 1, 1996 now U.S. Pat. No. 5,902,838, issued May 11, 1999.

FIELD OF THE INVENTION

The present invention pertains to sealed flat panel display devices, tonovel edge sealant compositions therefor and to novel polymers used insuch compositions.

BACKGROUND OF THE INVENTION

A variety of flat panel display devices are known including plasma andfield emission display devices. references describing such devicesinclude U.S. Pat. No. 4,857,799; U.S. Pat. No. 5,216,324; L. Branst andF. Pothoven, Semiconductor International, January 1996, p. 109; "TheGrand Alliance in Flat Panels," Business Week, Aug. 28, 1995, p. 73; andC. Curtin, "The Field Emission Display: A New Flat Panel Technology,"IDEC '91 pp. 12-15 (8/1991). The construction and operation of suchdevices vary but in general it is necessary to provide a high vacuum ina sealed interior volume between a base plate and a spaced face plate.The interior volume is defined and the vacuum maintained by an edgesealant which bonds the two plates together in spaced relationship.Current methods of vacuum sealing of flat panel displays require the useof solder glass frits as edge sealants. Such frits require long heatingperiods at 450-600° C. to melt and fuse the frit with the glass panelsof the display. There are, however, several problems associated withthis method including long processing times, thermal degradation ofcritical components during the heat sealing operation, difficulty inmaintaining micron size alignment tolerances under high heat conditionsand compatibility of the frits with display glass.

While there are a number of alternative edge sealing techniquesproposed, it is still desirable to obtain a commercially satisfactoryalternative to the glass frit sealant. In particular, it is desirable toobtain a sealant which can produce a fixtured assembly at lowtemperature, which can withstand high temperature bake out, and whichafter bakeout, pumpout and closure of the pumpout port, can maintain avacuum seal at pressures in the range of from about 10⁻³ Torr to about10⁻⁹ Torr, depending on the specific application, without outgassing.

Unmodified alkenyloxystyrene adhesives are disclosed in U.S. Pat. Nos.5,084,490 and 5,141,970 (McArdle et al) and in U.S. Pat. Nos. 4,543,397and 4,732,956 (Woods et al). Poly(4-allyloxystyrene) and somewhatrelated polymers are described in Frechet, et al, "Imaging processesbased on side-chain Modification of Polymers", ACS Symp. Ser.(1989), 381(Eff. Radiat. High-Technol. Polym.), 155-71, and in Chem. Abst.101:46315 (1984); 97:31277 (1982); 90:152895 (1979); 69:107140 (1968);and 67:11767 (1967). In all of these references the adhesives and otherpolymer systems are unfilled.

It is known that certain alkenyloxystyrene monomers, such as4-allyloxystyrene, can be cationically photocured to produce a solidcrosslinked polymer, which upon thermal baking will B-stage cure by aClaisen Rearrangement reaction to produce a polymeric material which hasvery high decomposition and glass transition temperatures. However, suchmonomers, and the adhesive compositions derived from these monomers,generally have very low viscosities compared to conventional adhesivesand sealants. The low viscosity characteristics of these materialssometimes present processing difficulties related to adhesive "run-off"during the assembly of the components to be bonded together. In suchcircumstances, the adhesive bead, applied to one surface, flows beyondthe intended bond or seal line area. This problem is particularly acutein those applications where assembly of the two substrates takes arelatively long time to complete after the application of the adhesive,such as is the case in the assembly of flat panel displays where precisealignment of the two substrates is a time consuming operation. Theresults of adhesive run-off include joint starvation with subsequentseal or adhesive failure, adhesive contamination and failure ofcontaminated components of the device to be sealed or bonded andincreased processing costs related to adhesive wastage and clean-up.

A well known technique for overcoming such rheological problems withother monomer-based adhesive and sealant systems is to dissolvepolymeric additives in the monomer composition, thus increasing theviscosity and minimizing or preventing the adhesive run-off duringassembly. However, it has been found that conventional polymericthickeners such as polystyrene do not possess adequate thermalresistance properties to be useful in alkenyloxystyrene compositionsintended for applications with high-temperature and/or high-vacuum,low-outgassing requirements. Furthermore, as illustrated in the examplesbelow, the corresponding polymers prepared by the conventionalpolymerization of 4-allyloxystyrene monomer have been found to beunsuitable due either to chemical instability (cationically polymerizedpolymer, see Example 4, composition C) or insolubility (free radicallypolymerized polymer, see Example 3).

Polymerization of 4-allyloxystyrene by means of free radical initiatorsis reported in J. Frechet et al, in ACS Symp. Ser. 381 (Eff. Radiat.High-Technol. Polym.), 155-71, (1989), and in Chem. Abst., 69:107140(1968) abstracting M. Kato et al, J. Polym. Sci., Part A-1, 6(11),2993-3006 (1968). JP 59034532 (abstract), reportedly describes ananionically polymerized 4-allyloxystyrene polymer. Such material wouldbe expected to inhibit cationic curing and therefore would be unsuitableas thickeners for cationically curable compositions.

SUMMARY OF THE INVENTION

The present invention addresses the need to provide alkenyloxystyreneadhesives and sealants with increased viscosities and improvedrheological control compared to the unfilled systems. The work isspecifically directed to compositions which are useful for the vacuumsealing of flat panel displays utilizing field emission cathodes,although the invention has application to other types of flat paneldisplay devices and to many other adhesive, sealant, coating and moldingcompound problems.

In one aspect the invention is a composition comprising:

a) a monomer component comprising at least one cationically curablemonomer and

b) a polymer component comprising at least one member selected from thegroup consisting of polymers of the formulae: ##STR1## where n is aninteger and R₁, R₂ and R₃ are H; or

R₁ is methyl and R₂ and R₃ are H; or

R₁ and R₂, are H and R₃ is methyl; or

R₁ is H and R₂ and R₃ are methyl, the polymer component being dissolvedin the monomer component and the composition being storage-stable.Particularly preferred compositions employ in the monomer component (a)a member selected from the group consisting of 4-allyloxystyrene,4-methallyloxystyrene, 4-crotyloxystyrene, 4-prenyloxystyrene (i.e.,4-(3-methyl-2-butenyloxy)styrene), 2-allyloxystyrene,2-methallyloxystyrene, 2-crotyloxystyrene or 2-prenyloxystyrene. Suchcompositions, thermally cured to a B-stage crosslinked polymer in themanner described herein, are capable of bonding and maintaining seal inflat panel display devices having internal pressures as low as 10⁻⁸Torr.

Another aspect of the invention is a process for producing a bondedassembly from two substrate components, at least one of the substratecomponents being transparent to UV light, the process comprising:

applying a bead of a curable composition of the invention about theperimeter of a predetermined area on a first of said two substratecomponents,

applying the second of said two substrate components to said bead toproduce a joined assembly having a volume enclosed by said twosubstrates and said bead;

irradiating the joined assembly with UV light through said at least onetransparent substrate component to polymerize said at least one monomer,thereby producing a fixtured assembly of the two substrate components;and subsequently,

heating the fixtured assembly to a temperature and for a time sufficientto cause rearrangement of the polymerized composition to a coloredB-stage crosslinked polymer.

Novel acid free polymers useful in the compositions as defined abovecomprise still another aspect of the invention. A still further aspectof the invention are flat panel display devices produced by the methodof the invention and/or by B-stage curing of compositions of theinvention. These and other aspects of the invention are set forth ingreater detail in the accompanying description and claims.

DESCRIPTION OF THE FIGURE

The figure is a partial side sectional view of a flat panel displaydevice of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The characteristics which make the inventive alkenyloxystyrene adhesivesuseful for the production of flat panel displays include highdecomposition and glass transition temperatures, low outgassing, rapidphotocure and good adhesive strength. The adhesives of the invention canbe easily used in preparing flat panel display devices because it hasbeen found that the monomer formulations can be thickened by dissolvingacid-free alkenyloxystyrene polymers which are soluble in the monomers.Such polymers can be prepared by alkylation of poly(4-hydroxystyrene)with an alkenyl functional alkylating agent such as allyl bromide,methallyl bromide, crotyl bromide or prenyl bromide.

Polymers so-prepared have the following characteristics:

1. they are soluble in alkenyloxystyrene monomers at a sufficiently highconcentration to increase the viscosity of the composition;

2. they do not result in a lowering of the decomposition temperature ofthe adhesive nor contribute to outgassing during cure or in subsequentuse;

3. they are chemically and physically stable in the uncured monomerblend; and

4. they do not interfere with nor inhibit the cationic cure mechanism ofthe alkenyloxystyrene composition.

The compositions of the invention include a cationically curable monomercomponent in addition to the polymer component. The monomer componentsuitably contains one or more of 4-allyloxystyrene,4-methallyloxystyrene, 4-crotyloxystyrene, 4-prenyloxystyrene,2-allyloxystyrene, 2-methallyloxystyrene, 2-crotyloxystyrene or2-prenyloxystyrene. 4-Allyloxystyrene is preferred. A particularlysuitable method of preparation of 4-allyloxystyrene utilizessaponification and alkylation of 4-acetoxystyrene, as described in U.S.Pat. No. 5,633,411, filed May 28, 1996, incorporated herein byreference. A monomer having two or more cationically curablecarbon-carbon double bonds may optionally also be employed in themonomer component of the composition at levels of from about 1 to about50%, preferably from about 10 to about 40% by weight of the monomercomponent. Suitable such monomers include commercially available divinylether monomers, distyryloxy compounds,2,2-bis(3-allyloxy-4-vinyloxyethoxyphenyl)propane and other monomersdisclosed in U.S. Pat. No. 5,070,117 and the "matrix" monomers describedin U.S. Pat. No. 5,141,970, both of which patents are incorporatedherein by reference.

The monomer/polymer ratio may be widely varied depending on theparticular requirements of the specific application to which thecomposition will be put. Suitable ratios of monomer to polymer rangefrom about 99:1 to about 5:95 on a parts by weight basis. For flat paneldisplay applications a monomer to polymer ratio of from 90:10 to 50:50is more preferred.

Where photocuring is desired for the A-stage cure of the composition, acationic photoinitiator which does not initiate substantialpolymerization of the allylic double bond of the monomer component mayalso be included in the composition. Suitable such photoinitiators andtheir effective amounts are well known. Typically they are employed at alevel within the range of 0.1-10% by weight of the composition,preferably 1-5% by weight. Generally such photoinitiators are iodonium,sulfonium, pyrylium, thiopyrylium or diazonium salts of a complexhalogenide. Examples include di-p-tolyl iodonium hexafluorophosphate,diphenyl iodonium hexafluoroarsenate, UVE 1014™ a sulfonium saltphotoinitiator sold by General Electric, and Cyracure UVI-6974, acationic photoinitiator sold by Union Carbide Corp.

The alkenyloxystyrene adhesive compositions address the problems ofglass frit edge sealants for flat panel display devices which have beendescribed above. They fixture on exposure to UV light following a fewseconds irradiation at low to moderate light intensities (A-stage cure).This provides a means of excellent control of the alignment process andeliminates the concerns regarding maintaining alignment tolerancesduring the subsequent heat cure cycle (B-stage cure). The typicalB-stage conditions involve heating the UV irradiated device at 150-250°C. for periods of approximately 1-3 hours. These conditions areconsiderably more favorable than the conditions necessary to fuse glassfrit, and thus they reduce the risk of thermal damage to critical devicecomponents during the sealing process. The cured alkenyloxystyrenecompositions have excellent adhesion to glass, provide adequate vacuumsealing of display devices and maintain mechanical and chemicalstability throughout the high temperature vacuum bake that is requiredto remove traces of contaminant gasses after the sealing is complete.

The polymer modification synthesis of poly(4-allyloxystyrene) involvingthe alkylation reaction of poly(4-hydroxystyrene) with allyl bromide inthe presence of excess potassium carbonate is illustrated in thereaction equation 1. ##STR2##

In addition to having good solubility in the alkenyloxystyrene monomercomponent of the inventive adhesives, the polymers of the presentinvention are capable of undergoing B-stage curing via a ClaisenRearrangement reaction at elevated temperatures which generates allylsubstituted phenolic side chain structure on the preexisting polymer.The resulting allyl functional phenolic polymer will promptly undergoacid catalyzed electrophilic addition reaction between the allylic groupand a phenol at the remaining available ortho or para position thereofyielding a colored polymer which is much more highly crosslinked. Thus,the B-stage chemistry of the polymer filled compositions is similar tothat of the unfilled systems and the cured products have similar goodthermal resistance properties comparable to the cured unfilled systems.

In addition to poly(4-allyloxystyrene), several similarly preparedpolymers, not previously reported, are also useful in the inventivecompositions. These include poly(4-methallyloxystyrene) (2),poly(4-crotyloxystyrene) (3) and poly(4-prenyloxystyrene) (4). ##STR3##

The syntheses of these materials are performed under similar conditionsto that described in example 1, but using methallyl bromide for polymer2, crotyl bromide for polymer 3 and prenyl bromide for polymer 4.Corresponding chloride or iodide compounds may be employed in place ofthe indicated bromides. It is also possible to obtain useful 2-alkenoxysubstituted polymers by the alkylation of poly(2-hydroxystyrene) withthe various halides, which are indicated by the generic structures inreaction equation (5). ##STR4##

Referring to the Figure there is shown therein a fragment of a flatpanel display device 10 which includes a face plate 12, a base plate 14with side wall 15 bonded thereto or integrally formed thereon, and acured adhesive layer 16 sealingly bonding the face plate and base platetogether along the upper edge of sidewall 15. Details of the internalstructure of the device are not shown as they are conventional and canvary significantly depending on the particular device. The device 10 maybe a plasma display, a field emission display or any other conventionaltype of flat panel display device. The adhesive layer 16, however, is aB-stage cured alkenyloxystyrene adhesive composition as describedherein. The device 10 may be prepared by assembling the face and baseplates in aligned spaced relationship with a layer of an adhesivecomposition of the invention applied to the upper surface of thesidewall 15 so as to contact and seal the interface between both plates.The device is provided with a sealable pumpout port, not shown, ofconventional design. UV cure of the adhesive while the alignment ismaintained, using conventional photocuring conditions, produces analigned bonded assembly which can then be removed from the alignmentfixturing. The assembly is subsequently placed in an oven, suitably at150-250° C. for 1-3 hours, to B-stage cure the adhesive layer and tobake off volatile contaminants. The interior is evacuated via thepumpout port during the bake cycle, after which the pumpout port issealed in conventional manner.

In an equivalent alternative embodiment, the sidewall may be formed aspart of the face plate, with the adhesive bead being applied between thelower edge of the sidewall and the base plate. In a still furtherembodiment the sidewall may be joined to one or the other of the faceand base plates using the adhesive of the invention, cured to at leastan A-stage cure, and then the other of the face and base plate bonded tothe resulting plate/sidewall assembly in the manner described above.

The compositions of the invention, particularly at higherpolymer/monomer ratios, may also be employed as curable gasket edgesealants for liquid crystal display devices.

In some applications thermal A-stage curing may be suitable, typicallyby heating the composition to a lower temperature and/or for a shorterperiod of time than is required for B-stage curing. Suitable thermalcatalysts for such applications are especially diazonium salts, althoughany of the cationic photoinitiators identified above may be alsoemployed as thermal initiators of cationic polymerization under somecircumstances. It is also possible in some applications of the inventiveadhesive to eliminate the separate A-stage curing step, producing ajoined assembly with a composition of the invention and then thermallycuring the composition directly to the B-stage.

While less preferred than the compositions previously described, curableadhesive formulations of a cationically curable monomer component andthe alkenyloxy etherified phenolic polymers described herein may alsousefully be prepared in which the monomer component contains noallyloxyoxystyrene monomer, especially where the polymer comprises themajority of the monomer/polymer composition. Examples of suchcationically curable monomers which do not have allyloxyoxystyrenefunctionality are divinyl ether compounds, for instance divinyl ethersof polyalkylene glycols, and distyryloxy compounds. Because of theability of the polymers employed in the inventive compositions toB-stage cure as described above, such compositions can have improvedthermal resistance properties compared to formulations of the samemonomers filled with conventional polymeric thickeners.

The invention is illustrated by the following non-limiting examples.

EXAMPLES Example 1 Synthesis of poly(4-allyloxystyrene) frompoly(4-hydroxystyrene)

To a 500 ml 3-necked flask equipped with a reflux condenser, mechanicalstirrer and addition funnel was added 100 mls acetone. Potassiumcarbonate (83.4 g) was added portionwise to the stirred reactor followedby poly(4-hydroxystyrene) (25.2 g; 0.21 moles of repeat units; weightaverage molecular weight (Mw)=9,700; molecular weight distribution(MWD)=2.4, supplied by Hoechst Celanese). After stirring for anadditional 15 minutes, a solution of allyl bromide (26.75 g; 0.22 moles)was added dropwise over 30 minutes and the mixture heated under refluxfor 4 hours. On cooling the reaction mixture was filtered and thesolvent removed under reduced pressure. Water (70 mls) was added to theresidue and the mixture extracted with dichloromethane (1×70 mls and1×30 mls). The combined dichloromethane extracts were dried over sodiumsulfate, filtered and the solution concentrated by partial distillationof the solvent under reduced pressure. The residue (28.17 g) wastransferred to a crystallizing dish and heated under vacuum (40° C., 76mm Hg) to constant weight to give poly(4-allyloxystyrene) as a faintyellow colored solid. (19.12 g, 57% yield). The structure of the polymerwas confirmed by spectroscopic and chromatographic analysis

¹ H NMR (CDCl₃): δ 6.6, m, 4H, aromatic protons; δ 6.1, m, 1H, --CH═CH₂; δ 5.1-5.5, m, 2H, --CH═CH₂ ; δ 4.5, m, 2H, --OCH₂ ; 1.1-1.9, m, 3H,--CH₂ CH.

IR (KBr disc): 1647 cm⁻¹, 926 cm⁻¹, allyl group.

GPC (PS standards, PL gel): Mw=13,200; MWD=3.0.

Example 2 (Comparative Example) Synthesis of poly(4-allyloxystyrene) byCationic Polymerization of 4-allyloxystyrene

4-Allyloxystyrene (0.860 g) and cationic photocatalyst Cyracure UVI 6974(Union Carbide) (0.017 g) were blended together to give an ultra-violet(UV) light sensitive solution. Several drops of the solution were placedon a glass plate to form a thin liquid film of approximately 0.25 mm inthickness. The supported monomer film solution was exposed to UV lightfrom an Oriel UV mercury light projector (model 87331) for 20 seconds(incident light intensity=30 mW/cm² at 365 nm) during which time theliquid monomer polymerized to give a dry, solid film ofpoly(4-allyloxystyrene) in quantitative yield. The IR spectrum of thepolymer was identical to that of the polymer produced by the method ofexample 1, thus confirming the polymer structure. Both the molecularweight and distribution were, however, significantly higher for thepolymer produced by this method.

GPC (PS standards, PL gel): M_(w) =88,800; MWD=3.8

Example 3 (Comparative Example) Synthesis of poly(4-allyloxystyrene) byFree Radical Polymerization of 4-allyloxystyrene

4-Allyloxystyrene (0.469 g) and free radical initiator2,2'-azobisisobutyronitrile (0.003 g, Aldrich Chemical Co.) were blendedtogether in a glass tube to give a thermally sensitive polymerizablesolution. The head space in the tube was purged with nitrogen andsealed. The tube heated at 100° C. for 0.5 hours and cooled. Thisprovided a soft rubber-like polymer that was insoluble in4-allyloxystyrene and several common organic solvents including acetoneand tetrahydrofuran. The polymer readily swelled in solvent indicatingthat a crosslinking polymerization reaction had occurred.

Example 4 Preparation of UV Photocurable Adhesives

UV light sensitive photocurable compositions were prepared by blendingtogether the materials listed below.

Composition A (monomer blend):

4-allyloxystyrene 15.010 g

2,2-bis(3-allyl-4-vinyloxyethoxyphenyl)propane (per U.S. Pat. No.5,070,117) 5.020 g

Cationic photocatalyst Cyracure UVI-6974 (Union Carbide Corp.) 0.282 g

This composition is a relatively low viscosity liquid with flowcharacteristics similar to water. On exposure to UV light thecomposition rapidly formed an insoluble, hard, crosslinked polymer. Theestimated tack-free cure time of a thin film of this adhesive is 5seconds at a UV light intensity of 30 mW/cm² (measured at 365 nm).

Composition B (invention formulation):

monomer blend (composition A) 1.010 g

poly(4-allyloxystyrene) (synthesized by the method of example 1) 0.330 g

The polymer readily dissolved in the monomer to form a slightly hazysolution. The solution has a relatively high viscosity compared tocomposition A as evidenced by its greater resistance to flow. Thesolution is stable with respect to dark thermal polymerization andshowed no signs of deterioration on storage at room temperature for 4weeks. On exposure to UV light the composition rapidly formed aninsoluble, crosslinked polymer which was softer and more flexible thanthe cured material of composition A. The estimated tack-free cure timeof a thin film of this adhesive is 10 seconds at a UV light intensity of30 mW/cm² (measured at 365 nm).

Composition C (comparative formulation):

4-allyloxystyrene 0.223 g

poly(4-allyloxystyrene) (synthesized by the method of example 2) 0.077 g

The monomer instantly polymerized following the addition of the polymer.The polymerization reaction was so rapid that complete solution of thepolymer was not achieved. This result demonstrates that polymer producedby the method of example 2 is unsuitable for use in compositionscontaining 4-allyloxystyrene monomers.

Composition D (comparative formulation):

monomer blend (composition A) 9.00 g

poly(styrene), Mw ˜45,000 (Aldrich) 3.00 g

The polystyrene was dissolved in the monomer blend by stirring at 30° C.for 3 hours. A slightly hazy solution was obtained with flowcharacteristics that were similar to composition B. On exposure to UVlight the composition gave an insoluble crosslinked polymer.

Example 5 Thermal Analysis of Poly(4-allyloxystyrene) and Various UVCured Compositions

The thermal properties of poly(4-allyloxystyrene) prepared as describedin Example 1 and the UV cured compositions A, B and D of Example 4 weredetermined by dynamic thermal gravimetric analysis (TGA) in which theweight loss was recorded as a function of temperature. The analyses wereconducted under a nitrogen atmosphere at a heating rate of 10°C./minute. The thermal resistance properties were defined in terms ofthe temperature of the onset of degradation (T_(d)) (i.e. thetemperature at which the polymer begins to loose weight as determined bystep analysis of weight loss temperature profile) and the weight lossmeasured at 400° C. The results are presented in Table 1.

                  TABLE 1                                                         ______________________________________                                        TG analyses of poly(4-allyloxystyrene) (PAOS) and UV cured                    compositions with and without added PAOS and poly(styrene) (PS)                                             Weight loss                                     Composition         T.sub.d (° C.)                                                                   at 400° C. (%)                           ______________________________________                                        poly(4-allyloxystyrene) (PAOS)                                                                    431       2                                               (example 1)                                                                   UV cured monomer blend without PAOS                                                               430       2                                               (composition A, example 4)                                                    UV cured monomer blend with PAOS                                                                  431       4                                               (composition B, example 4)                                                    UV cured monomer blend with PS                                                                    305       14                                              (composition D, example 4)                                                    ______________________________________                                    

The results demonstrate that high decomposition temperatures and lowweight losses associated with cationically polymerized 4-allyloxystyrenemonomers are not significantly reduced when poly(4-allyloxystyrene) isused to control the rheology of the composition. In contrast, theconventional polymeric modifier, polystyrene, results in a significantreduction in the onset of degradation temperature of the composition anda corresponding large weight loss at 400° C. The outgassing associatedwith this latter composition makes it unsuitable for the sealing of flatpanel FED displays.

In the report by J. Frechet et al, ACS Symp. Ser. 381, 155, (1989), itis stated that the thermal degradation of poly(4-allyloxystyrene)resembles that of poly(4-hydroxystyrene). Unexpectedly it has been foundthat the thermal degradation of poly(4-allyloxystyrene) used in thiswork occurs at a significantly higher temperature than that of thestarting polymer (see Table 2).

                  TABLE 2                                                         ______________________________________                                        TG analyses of poly(4-hydroxystyrene) and                                     poly(4-allyloxystyrene) (PAOS)                                                                            Weight loss                                       Composition        T.sub.d (° C.)                                                                  at 400° C. (%)                             ______________________________________                                        poly(4-hydroxystyrene)                                                                           325      75                                                (literature report)                                                           poly(4-hydroxystyrene)                                                                           374      50                                                (example 1)                                                                   poly(4-allyloxystyrene) (PAOS)                                                                   431       2                                                (example 1)                                                                   ______________________________________                                    

While this invention may be embodied in many different forms, there areshown in the drawings and described in detail herein specific preferredembodiments of the invention. The present disclosure is anexemplification of the principals of the invention and is not intendedto limit the invention to the particular embodiments illustrated.

This completes the description of the preferred and alternateembodiments of the invention. Those skilled in the art may recognizeother equivalents to the specific embodiment described herein whichequivalents are intended to be encompassed by the claims attachedhereto.

What is claimed is:
 1. A process for producing a bonded assembly fromtwo substrate components, at least one of the substrate components beingtransparent to UV light, the process comprising:applying a compositioncomprising:a) a monomer component comprising at least one memberselected from the group consisting of 4-allyloxystyrene,4-methallyloxystyrene, 4-crotyloxystyrene, 4-prenyloxystyrene,2-allyloxystyrene, 2-methallyloxystyrene, 2-crotyloxystyrene or2-prenyloxystyrene, b) a substantially linear polymer component having aformula consisting essentially of repeat units selected from the groupconsisting of ##STR5## where R₂, R₂ and R₃ are H; orR₁ is methyl and R₂and R₃ are H; or R₁ and R₂, are H and R₃ is methyl; or R₁ is H and R₂and R₃ are methyl, and c) a cationic photoinitiator,the polymercomponent being dissolved in the monomer component and the compositionbeing storage-stable, to at least one of the substrate components;joining the two substrate components in desired alignment to produceajoined assembly; irradiating the joined assembly with UV light throughsaid at least one transparent substrate component to polymerize saidmonomer component, thereby producing a fixtured assembly of the twosubstrate components; and subsequently, heating the fixtured assembly toa temperature and for a time sufficient to cause rearrangement of thepolymerized composition to a colored B-stage crosslinked polymer.
 2. Amethod as in claim 1 wherein said joined assembly is formed with a gapbetween the two substrate components, the composition being applied soas to form a perimeter around at least a portion of the joined assemblyand thereby define an enclosed volume between said two substratecomponents, and wherein said enclosed volume is evacuated and sealedbetween said irradiation step and said heating step.
 3. A method as inclaim 2 wherein said bonded assembly is a flat panel display device. 4.A flat panel display device having a face plate and a base plateseparated by a sealed and evacuated gap, the gap being sealed by B-stagecuring of a composition comprising:a) a monomer component comprising atleast one member selected from the group consisting of4-allyloxystyrene, 4-methallyloxystyrene, 4-crotyloxystyrene4-prenyloxystyrene, 2-allyloxystyrene, 2-methallyloxystyrene,2-crotyloxystyrene or 2-prenyloxystyrene, and b) a substantially linearpolymer component having a formula consisting essentially of repeatunits selected from the group consisting of ##STR6## where R₁, R₂ and R₃are H; orR₁ is methyl and R₂ and R₃ are H; or R₁ and R₂, are H and R₃ ismethyl; or R₁ is H and R₂ and R₃ are methyl, the polymer component beingdissolved in the monomer component and the composition beingstorage-stable.
 5. A bonding process comprising:a) applying acomposition comprising a storage-stable solution of:at least onecationically polymerizable monomer and a polymeric thickener of theformula: ##STR7## where n is an integer and R₁, R₂ and R₃ are H; orR₁ ismethyl and R₂ and R₃ are H; or R₁ and R₂, are H and R₃ is methyl; or R₁is H and R₂ and R₃ are methyl,the composition further comprising athermal or photo activated cationic initiator, to a first substrate, b)contacting a second substrate to the composition on the first substrateto produce a joined assembly, and subsequently c) thermally curing thecomposition to a B-stage polymer.
 6. A bonding process as in claim 5wherein the composition is cured to an A-stage polymer by cationicpolymerization of the cationic monomer in a first curing stage, andthen, in a second curing stage is thermally cured to said B-stagepolymer.
 7. A bonding process as in claim 6 wherein the composition iscured to said A-stage polymer by cationic thermal curing of the cationicmonomer at a first time and temperature in said first curing stage, andthen is cured to said B-stage polymer in said second curing stage byheating the composition to a higher temperature and/or for a longerperiod of time than said first curing stage.
 8. A bonding process as inclaim 6 wherein the joined assembly is held together with a fixturingapparatus during said first curing stage, said fixturing apparatus beingremoved between said first and second curing stages.
 9. A bondingprocess as in claim 6 wherein said composition is cured to said A-stagepolymer by cationic photopolymerization of the cationicallypolymerizable monomer.